CRYSTALS OF SOLUBLE INTERLEUKIN-1 RECEPTOR COMPLEXED WITH ITS NATURALANTAGONIST REVEAL A 1 1-RECEPTOR-LIGAND COMPLEX/

Interleukin-1 is a cytokine involved in the acute phase response again st infection and injury, We obtained crystals of a complex of soluble, recombinant human interleukin-l receptor and recombinant human interl eukin-l receptor antagonist, a naturally occurring antagonist. The cry stals are suitable for X-ray analysis and diffract to 2.7 Angstrom res olution, Solvent content calculations indicate that the crystals conta in one receptor and one antagonist molecule per asymmetric unit, Other receptor to antagonist ratios are highly unlikely, These results sugg est that the interleukin-1 antagonist binds a single receptor molecule and does not cause receptor aggregation.